Air core motor-generators have the potential to provide higher efficiency and performance than conventional type electrical machines. They achieve these advantages by eliminating slot wound armature windings wherein the windings are wound in slots in a steel stator, and instead locate the windings within the magnetic airgap. Air core motor-generators can utilize single rotating or double rotating construction. Single rotating construction utilizes a loss mitigating ferromagnetic stator on one side of the airgap. Double rotating air core motor-generators eliminate the need to pass a circumferentially varying flux through a ferromagnetic stator by bounding both sides of the magnetic airgap by rotating surfaces of the rotor.
Various different methods for constructing air core armatures have been utilized along with different winding pattern configurations. Even further increased efficiency and power capability with air core motor-generators is desired.
It has been found through experience that the use of Litz wire windings for the armatures of air core motor-generators is in many cases less than optimal. Litz wire can successfully reduce eddy current losses from transverse penetrating flux from the rotor poles due to the small conductor cross-section size. Litz wire also has a maximum theoretical packing factor of about 90% that should allow high efficiency. However, it has been found that a practically achievable packing factor is lower than the theoretical value. Packing factors of about 55% are more typical. In addition, compaction of Litz wire is difficult without the use of a high compression force on the windings. This compaction force requirement makes manufacturing of air core armatures more difficult and is undesirable.